This invention relates to a method and apparatus for controlling the orientation of a tool, and more particularly a method and apparatus for controlling the orientation of a tool so as to coincide the orientation with the direction of movement of a spindle at the start thereof prior to the actual movement of the spindle which is caused by a datum regarding the movement of the tool relative to a workpiece.
In a working machine wherein a sheet shaped workpiece is cut along a predetermined profile, or in a fret saw machine in which during cutting of a sheet blank the fret saw blade is reciprocated in the vertical direction while at the same time the orientation of the fret saw blade is constantly controlled such that it is tangential to a predetermined cutting profile, it is generally necessary to always orient the tool in the tangential direction with respect to the cutting profile during the cutting operation in addition to moving the tool with respect to the workpiece.
For the sake of description a fret saw machine will be taken as an example of such working machines.
Where a groove having a predetermined profile is cut through a die board, with a prior art fret saw machine a profile curve is drawn on the die board and an operator rotates the die board on a table such that the fret saw blade is always oriented tangentially with respect to the profile. In this case, the fret saw blade itself would not be rotated.
However, when the area of the die board is large, it is difficult for the operator to accurately and rapidly follow the profile drawn on the die board. Furthermore, it is difficult to employ skilled workmen. For these reasons, it has been desired to automate a fret saw machine for working die boards.
There has already been proposed a numerical control device for accurately executing a contouring of a tool with respect to a workpiece as in an NC machine tool. However, the cutting tool utilized in the NC machine tool is generally rotated by the spindle thereof and the axis of the tool is guided along a contour and it is not necessary to control the orientation of the tool.
In an optical profiling machine, there is provided a head with a servomechanism which follows a given profile curve and the orientation of a tool is controlled in an electrically interlocked relationship with the head. However, such machine cannot follow the profile curve when it contains one or more discontinuities.